Hyperthermia

HYPERTHERMIA, HYPOTHERMIA, see Thermoregulation. HYPERTHYROIDISM, HYPOTHYROIDISM, conditions of the organism that result from increased (hyper-) or, conversely, weakened (hypo-) internal secretory activity of the thyroid gland (see also Athyrosis, Basedow's disease, Dysthyroidism, Goiter, Myxedema, Thyroxin and Thyroid gland).-The condition of hypothyroidism in many respects corresponds to the picture of athyrosis, differing from it in lesser intensity and expressiveness of symptoms. All physiological processes are depressed due to insufficient secretion by the thyroid gland of its hormone-thyroxin. The cause of such a decrease in thyroid function may be either functional, congenital or acquired (intoxications, disturbances of secretory innervation), or organic disorders in the form of absence or destruction of part of the gland or in the form of degenerative processes in it (colloid and fibrous goiters). The younger the organism in which a disturbance of thyroid function has occurred, the more sharply the signs of hypothyroidism manifest themselves: retardation of growth (mainly in length), underdevelopment of the sex glands, mental lethargy, mental retardation (infantilism), insufficiently intense metabolism, accompanied by a tendency to obesity and hydrophilia (Epstein), hypothermia. General disturbance of trophics, in addition to external signs (dry, coarse skin, delayed eruption and replacement of teeth, dystrophy of hair and nails, delayed development of ossification nuclei and bone growth in length), is also manifested in decreased resistance to infections (hypotrophy of the physiological system of connective tissue). Mild, hidden forms of hypothyroidism can be recognized only by studying the metabolism (characteristic decrease in basal metabolism), and

thanks to the success in the use of thyroid gland preparations. The predominance in individual cases of hypothyroidism of some symptoms over others depends on the constitutional state of individual physiological systems, on their greater or lesser sensitivity to lack of thyroid hormone. Experimental reproduction of hypothyroidism by removal of part of the thyroid gland in animals is not an easily achievable task: apparently even extensive resections of the organ (especially in adult animals) are easily compensated by the remaining at least small part of the gland (accessory thyroid glands); in these cases, minor changes in metabolism (decrease in basal metabolism) are most frequently found. On the basis of microscopic changes in the pituitary gland after complete or partial removal of the thyroid gland in adult animals, its vicarious activity is assumed. For differential diagnosis (rickets, exudative diathesis) and therapy of hypothyroidism, the indispensable services are provided by the administration of organ-preparations of the thyroid gland, first of all thyroxin. The picture of hyperthyroidism in many respects resembles the picture of Basedow's disease. Most of the symptoms of the latter fit into the clinical picture of experimental hyperthyroidism, developing as a result of prolonged administration of sufficient doses of thyroid gland preparations into the organism. Increased excitability of the nervous system is found; amphotonism (i.e., simultaneous hyper-, vago- and sympathicotonia) with predominance of hypersympathicotonia; the latter in hyperthyroidism is more correctly defined as a neurosis, irritable weakness of the sympathetic system-as a consequence of it tachycardia (often arrhythmias) is observed. In contrast to hypothyroidism, which proceeds with phenomena of anemia, the number of erythrocytes in hyperthyroidism is normal or even above normal. A constant finding is increased metabolism, manifested in enhanced breakdown of proteins, oxidation of fats (significant increase in basal metabolism). From the side of the liver, an increase in its urea-forming and diastatic function is noted. Due to decreased tolerance to carbohydrates, which in hyperthyroidism are probably subject to improper breakdown, hyperglycemia and glycosuria easily develop. Diuresis is increased. Heat production is increased, and since it is not simultaneously compensated by the increasing (almost always) heat elimination in hyperthyroidism, body temperature is often above normal. The organism loses weight. The basis of the clinical forms of hyperthyroidism lies either in functional moments (change in innervation) or in hyperplastic processes (Basedow's goiter), with heredity playing a large ROLE. L. Perelman.